1. Field of the Invention
The present invention relates generally to an electrical circuit for controlling a hydraulic winch used on an ocean going vessel. More particularly, the present invention relates to an electrical circuit which controls the operation of a hydraulic winch to prevent damage to the winch when the winch is being used to retrieve a winch cable.
2. Description of the Prior Art
Ocean going vessels, such as ships, barges and the like, routinely use hydraulic winches to retrieve tow or winch cables which have electrical equipment such as transducers, acoustic sensors, non acoustic sensor, etc. attached thereto. When a winch cable is being retrieved using a hydraulic winch damage will often occur to the equipment if the winch and thus cable are not stopped in time by an operator. Generally, the operator cannot be relied upon to prevent damage since at the end of travel of the cable, a very small movement of the winch drum can cause an overrun of the cable beyond its normal stop position resulting in damage to the cable and the equipment attached thereto.
Presently, to prevent the winch cable from moving beyond its normal stop position (causing damage to equipment and the winch cable) a limit switch control circuit 9 of the type illustrated in FIG. 1 is being utilized. The circuit 9 of FIG. 1 includes a limit switch 10 and a complex electronics circuit 12. The limit switch 10 is positioned so that its contact opens when a tow bar located at the end of the winch cable engages the limit switch 10 opening limit switch 10. When the limit switch 10 opens, the electronics b) circuit 12 turns off current flow to a winch electronic displacement controller 14 which stops the winch.
The electronics circuit 12 includes relays, comparators and other electrical components to de-energize the displacement controller 14. The electrical components of electronics circuit 12, however, are subject to failure which could result in substantial damage to the winch, the tow line and the electrical component attached to the tow line. In addition, the electronics circuit 12 is expensive resulting in substantial cost to the user when any of the electrical components of circuit 12 fail.
Accordingly, there is a need for a highly reliable yet relatively inexpensive circuit for de-energizing the winch electronic displacement controller to prevent the winch cable from moving beyond its normal stop position.
The hydraulic winch limit switch circuit of the present invention overcomes some of the difficulties of the prior art including those mentioned above in that it is a very simple, yet highly effective circuit for preventing a winch cable from moving beyond its normal stop position which insures that the winch cable and research equipment attached to the cable are not damaged.
The present invention is a relatively simple circuit which includes a single pole limit switch with a diode connected across the contact of the limit switch. In normal operation the limit switch is closed and current flow is through switch to a winch electronic displacement controller which controls the operation of the winch motor and the winch. When the winch reaches a stop position during payin of the winch cable, the limit switch opens as the result of the limit switch arm engaging a tow bar attached to the end of the winch cable. Opening the limit switch stops current flow through the winch electronic displacement controller since the diode is reversed biased during payin of the winch cable. This de-energizes the winch motor preventing the winch cable from moving beyond its normal stop position.
When there is payout of the winch cable, the diode is forward biased resulting in current flow through the diode to the winch electronic displacement controller which energizes the winch motor allowing for deployment of the winch cable.